If you use both screen and emacs regularly, you can save yourself a lot of aggravation by changing the screen escape character. For example, add something like this to your .screenrc:

escape ^Zz

This changes the prefix for all screen keystrokes from C-a to C-z. C-z is a good choice for two reasons. First, it's not mapped to anything I regularly use in emacs. But it also works for me since C-z C-d detachs from a screen session, which is one of the more common things I do in screen sessions, and I associate it with suspending a process with C-z.